Perform mean over the third dimension of the loop data.
loop_stochav(loop, nstoch_to_avg = "all")'raw_cf' container with loop data
String or integer, number of stochastic samples
to average over. Only possible string is 'all'.
If an integer is supplied, it must be at least '1'
and at most consistent with the number of stochastic
samples in loop.
Returns the input loop object with named elemens data and
dim added.